This study examines the impact of ideological cleavages on vote choice in South Korea’s 2025 presidential by-election. Acknowledging the limitations of the traditional, unidimensional spectrum of ideology in capturing the complexity of contemporary Korean voter ideology, the study employs multidimensional item response theory (MIRT) using multiple policy attitude questions. The analysis identifies two distinct ideological dimensions: economic-security and socio-cultural. Results show that voters for Lee Jae-myung(Democratic Party of Korea) and Kim Moon-soo(People Power Party) are relatively well-separated along the economic-security dimension yet overlap to a meaningful extent around the ideological center. Conversely, voters for Junseok Lee, a candidate from a newly established party, cluster near the center on the economic-security dimension yet exhibit pronounced conservatism on socio-cultural issues. Notably, young voters demonstrate heightened ideological differentiation, particularly on the socio-cultural dimension. Statistical analyses confirm that voter choice is influenced not only by economic-security issues but also significantly by socio-cultural ideological orientations. These findings suggest that the ideological structure of Korean politics is extending beyond traditional economic-security concerns toward socio-cultural issues, highlighting the emergence of a new political cleavage and potential ideological realignment among voters.
Sejin Koo (Sun,) studied this question.